Support cmdline_args when sys_exec.

os/src/trap/context.rs

@@ -1,6 +1,7 @@
 use riscv::register::sstatus::{Sstatus, self, SPP};
 
 #[repr(C)]
+#[derive(Debug)]
 pub struct TrapContext {
     pub x: [usize; 32],
     pub sstatus: Sstatus,

os/src/trap/mod.rs

@@ -88,6 +88,7 @@ pub fn trap_handler() -> ! {
             panic!("Unsupported trap {:?}, stval = {:#x}!", scause.cause(), stval);
         }
     }
+    //println!("before trap_return");
     trap_return();
 }